Semiconductor structure with enlarged gate electrode structure and method for forming the same

ABSTRACT

A semiconductor structure and a method for forming the same are provided. The semiconductor structure includes a gate stack structure formed over a substrate. The gate stack structure includes a gate electrode structure having a first portion and a second portion and a first conductive layer below the gate electrode structure. In addition, the first portion of the gate electrode structure is located over the second portion of the gate electrode structure, and a width of a top surface of the first portion of the gate electrode structure is greater than a width of a bottom surface of the second portion of the gate electrode structure.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers of material over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon.

One of the important drivers for increased performance in asemiconductor structure is the higher levels of integration of circuits.This is accomplished by miniaturizing or shrinking device sizes on agiven chip. Tolerances play an important role in being able to shrinkdimensions on a chip.

However, although existing semiconductor manufacturing processes havegenerally been adequate for their intended purposes, as devicescaling-down continues, they have not been entirely satisfactory in allrespects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It shouldbe noted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A to 1P are perspective views of various stages of forming asemiconductor structure in accordance with some embodiments.

FIG. 2 is a cross-sectional representation of the semiconductorstructure illustrated along line A-A′ shown in FIG. 1P in accordancewith some embodiments.

FIGS. 3A to 3B are cross-section representations of forming asemiconductor structure in accordance with some embodiments.

FIGS. 4A to 4B are cross-section representations of forming asemiconductor structure 100 c in accordance with some embodiments.

FIGS. 5A to 5B are cross-section representations of forming asemiconductor structure in accordance with some embodiments.

FIGS. 6A to 6D are cross-sectional representations of various stages offorming a semiconductor structure in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments of semiconductor structures and methods for forming the sameare provided. The semiconductor structure may include a gate stackstructure including a conductive layer and a gate electrode structureformed over the conductive layer. Before the gate electrode structure isformed, some portions of the conductive layer are etched back, so thatthe space for forming the gate electrode structure can be enlarged.

FIGS. 1A to 1P are perspective views of various stages of forming asemiconductor structure 100 a in accordance with some embodiments. Asshown in FIG. 1A, a substrate 102 is received in accordance with someembodiments. Substrate 102 may be a semiconductor wafer such as asilicon wafer. Alternatively or additionally, substrate 102 may includeelementary semiconductor materials, compound semiconductor materials,and/or alloy semiconductor materials. Examples of the elementarysemiconductor materials may be, but are not limited to, crystal silicon,polycrystalline silicon, amorphous silicon, germanium, and/or diamond.Examples of the compound semiconductor materials may be, but are notlimited to, silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide. Examples of thealloy semiconductor materials may be, but are not limited to, SiGe,GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP.

In addition, substrate 102 may include structures such as doped regions,interlayer dielectric (ILD) layers, conductive features, and/orisolation structures. Furthermore, substrate 102 may further includesingle or multiple material layers to be patterned. For example, thematerial layers may include a silicon layer, a dielectric layer, and/ora doped poly-silicon layer.

A dielectric layer 104 and a mask layer 106 are formed over substrate102, and a photo-sensitive layer 108 is formed over mask layer 104, asshown in FIG. 1A in accordance with some embodiments. Dielectric layer104 may be used as an adhesion layer between substrate 102 and masklayer 106. In addition, dielectric layer 104 may also be used as an etchstop layer for etching mask layer 106. In some embodiments, dielectriclayer 104 is made of silicon oxide. Dielectric layer 104 may be formedby using a thermal oxidation process, although other depositionprocesses may be used in some other embodiments.

Mask layer 106 may be used as a hard mask during subsequentphotolithography processes. In some embodiments, mask layer 106 is madeof silicon nitride. Mask layer 106 may be formed by using low-pressurechemical vapor deposition (LPCVD) or plasma enhanced chemical vapordeposition (PECVD), although other deposition processes may also be usedin some other embodiments.

Next, a fin structure 110 is formed by sequentially etching mask layer106, dielectric layer 104, and substrate 102 through photo-sensitivelayer 108, as shown in FIG. 1B in accordance with some embodiments.Afterwards, photo-sensitive layer 108 is removed.

After fin structure 110 is formed, an insulating layer 112 is formed tocover fin structures 110 over substrate 102, as shown in FIG. 1C inaccordance with some embodiments. In some embodiments, insulating layer112 is made of silicon oxide, silicon nitride, silicon oxynitride,fluoride-doped silicate glass (FSG), or other low-K dielectricmaterials. Insulating layer 112 may be formed by using ahigh-density-plasma (HDP) CVD process, although other depositionprocesses may be used in other embodiments.

Next, insulating layer 112 is recessed to form an isolation structure114, such as a shallow trench isolation structure, around fin structure110, as shown in FIG. 1D in accordance with some embodiments. Insulatinglayer 112 may be recessed by a wet etching process or a dry etchingprocess. In addition, mask layer 106 and dielectric layer 104 areremoved.

Afterwards, a dummy gate structure 116 is formed across fin structure110 and extends over isolation structure 114. In some embodiments, dummygate structure 116 includes a dummy gate dielectric layer 118 and adummy gate electrode layer 120 formed over dummy gate dielectric layer118. In some embodiments, dummy gate dielectric layer 118 is made ofsilicon oxide. In some embodiments, dummy gate electrode layer 120 ismade of polysilicon.

After dummy gate structure 116 is formed, spacers 122 are formed on thesidewalls of dummy gate structure 116 in accordance with someembodiments. In some embodiments, spacers 122 are made of siliconnitride, silicon oxide, silicon oxynitride, silicon carbide, or otherapplicable dielectric materials. Spacers 122 may include a single layeror multiple layers.

Next, source/drain structures 124 are formed in fin structure 110, asshown in FIG. 1E in accordance with some embodiments. In someembodiments, portions of fin structure 110 adjacent to dummy gatestructure 116 are recessed to form recesses at two sides of finstructure 110, and a strained material is grown in the recesses by anepitaxial (epi) process to form source/drain structures 124. Inaddition, the lattice constant of the strained material may be differentfrom the lattice constant of substrate 102. In some embodiments,source/drain structures 124 include Ge, SiGe, InAs, InGaAs, InSb, GaAs,GaSb, InAlP, InP, or the like.

After source/drain structures 124 are formed, a contact etch stop layer(CESL) 126 is formed over substrate 102, and an inter-layer dielectric(ILD) layer 128 is formed over contact etch stop layer 126, as shown inFIG. 1F in accordance with some embodiments. In some embodiments,contact etch stop layer 126 is made of silicon nitride, siliconoxynitride, and/or other applicable materials. Contact etch stop layer126 may be formed by plasma enhanced CVD, low pressure CVD, ALD, orother applicable processes.

Inter-layer dielectric layer 128 may include multilayers made ofmultiple dielectric materials, such as silicon oxide, silicon nitride,silicon oxynitride, phosphosilicate glass (PSG), borophosphosilicateglass (BPSG), and/or other applicable low-k dielectric materials.Inter-layer dielectric layer 128 may be formed by chemical vapordeposition (CVD), physical vapor deposition, (PVD), atomic layerdeposition (ALD), spin-on coating, or other applicable processes.

Next, a polishing process is performed on inter-layer dielectric layer128 and contact etch stop layer 126 to expose the top surface of dummygate structure 116 in accordance with some embodiments. In someembodiments, a chemical mechanical polishing (CMP) process is performeduntil the top surface of dummy gate structure 116 is exposed.

After the polishing process is performed, dummy gate structure 116 isremoved, such that a trench 130 a is formed, as shown in FIG. 1G inaccordance with some embodiments. As shown in FIG. 1G, trench 130 a isformed in interlayer dielectric layer 128 over substrate 102. In someembodiments, dummy gate structure 116 is removed by performing a dryetching process. In some embodiments, dummy gate structure 116 isremoved by performing a dry etching process and a wet etching process.In order to miniaturize or shrink device sizes on a given substrate, thedummy gate may have a relatively small width. Therefore, the resultingtrench 130 a may also have a relatively small width. In someembodiments, trench 130 a has a width in a range from about 10 nm toabout 25 nm.

After dummy gate structure 116 is removed, a gate dielectric layer 132is formed lining trench 130 a, as shown in FIG. 1H in accordance withsome embodiments. As shown in FIG. 1H, gate dielectric layer 132 isformed the sidewalls and the bottom surface of trench 130 a. In someembodiments, gate dielectric layer 132 is made of silicon oxide. In someembodiments, gate dielectric layer 132 is made of high-k dielectricmaterials, such as metal oxides, metal nitrides, metal silicates,transition metal-oxides, transition metal-nitrides, transitionmetal-silicates, or oxynitrides of metals. Examples of the high-kdielectric material include, but are not limited to, hafnium oxide(HfO₂), hafnium silicon oxide (HfSiO), hafnium silicon oxynitride(HfSiON), hafnium tantalum oxide (HfTaO), hafnium titanium oxide(HfTiO), hafnium zirconium oxide (HfZrO), zirconium oxide, titaniumoxide, aluminum oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, orother applicable dielectric materials.

Afterwards, a conductive layer 134 is formed over gate dielectric layer132, as shown in FIG. 1H in accordance with some embodiments. As shownin FIG. 1H, conductive layer 134 is formed over the sidewalls and thebottom of trench 130. In some embodiments, conductive layer 134 is ametal layer. In some embodiments, conductive layer 134 is made of a workfunction metal, which is configured to have a proper work function. Insome embodiments, conductive layer 134 is made of Ti_(x)N_(y), W,Ti_(x)Al_(y), Ti_(x)Al_(y)N, Ta_(x)Al_(y), Ta_(x)Al_(y)N_(z),Ti_(x)Si_(y)N_(z), Ta_(x)Si_(y)N_(z), Ta_(x)N_(y), Hf_(x)O_(y),Ti_(x)Ta_(y)N_(z). In some embodiments, conductive layer 134 has athickness in a range from about 1 Å to about 500 Å.

After conductive layer 134 is formed, another conductive layer 136 isformed over conductive layer 134, as shown in FIG. 1H in accordance withsome embodiments. In some embodiments, conductive layer 134 andconductive layer 136 are made of different materials. In someembodiments, conductive layer 134 and conductive layer 136 are made ofdifferent materials which have relative high etching selectivity in awet etching process.

In some embodiments, conductive layer 136 is a metal layer. In someembodiments, conductive layer 136 is made of a work function metal,which is configured to have a proper work function. In some embodiments,conductive layer 136 is made of Ti_(x)N_(y), W, Ti_(x)Al_(y),Ti_(x)Al_(y)N, Ta_(x)Al_(y), Ta_(x)Al_(y)N_(z), Ti_(x)Si_(y)N_(z),Ta_(x)Si_(y)N_(z), Ta_(x)N_(y), Hf_(x)O_(y), Ti_(x)Ta_(y)N_(z). In someembodiments, conductive layer 136 has a thickness in a range from about1 Å to about 500 Å.

After conductive layers 134 and 136 are formed, a hard mask layer 138 ais formed over conductive layer 136, as shown in FIG. 1I in accordancewith some embodiments. As shown in FIG. 1I, trench 130 a is filled withhard mask layer 138. In some embodiments, hard mask layer 138 is made ofcarbon-based materials, oxide based materials, silicon based materials,or combinations thereof.

Next, a first etching process 140 a is performed on hard mask layer 138,as shown in FIG. 1J in accordance with some embodiments. In someembodiments, first etching process 140 a is a dry etching process.During first etching process 140 a, the portion of hard mask layer 138 apositioned in the upper portion of trench 130 a is removed, so that ablocking structure 142 a is formed, as shown in FIG. 1J in accordancewith some embodiments. After first etching process 140 a, blockingstructure 142 a is formed in the lower portion of trench 130 a, suchthat the portion of conductive layer 136 formed at the lower portion oftrench 130 a is covered by blocking structure 142 a while the portion ofconductive layer 136 formed at the upper portion 131 a of trench 130 aare exposed.

After blocking structure 142 a is formed, the portion of conductivelayer 136 which is not covered by blocking structure 142 a is etched bya second etching process 144 a, as shown in FIG. 1K in accordance withsome embodiments. In some embodiments, second etching process 144 a is awet etching process. As described previously, conductive layers 134 and136 are made of different materials. However, since conductive layers134 and 136 are both made of conductive materials such as metals, theymay have poor etching selectivity in a dry etching process. Therefore, awet etching process is performed to remove the portion of conductivelayer 136 not covered by blocking structure 142 a, so that only a smallamount of conductive layer 134 formed below conductive layer 136 will beetched during the wet etching process in accordance with someembodiments.

In addition, when conductive layer 136 is etched by performing secondetching process 144, which is a wet etching process, conductive layer136 has a sloped (inclined) top surface. The sloped top surface mayenable the filling of gate electrode material become easier (Detailswill be described later.)

After second etching process 144 a is performed, blocking structure 142a is removed to expose lower portion 133 a of trench 130 a, as shown inFIG. 1L in accordance with some embodiments. As shown in FIG. 1L, afterblocking structure 142 a is removed, trench 130 a has a funnel shapewith a wider upper portion 131 a in a cross-sectional view.

Next, a gate electrode layer 146 a is formed over substrate 102, asshown in FIG. 1M in accordance with some embodiments. More specifically,gate electrode layer 146 a is formed over conductive layers 134 and 136,and upper portion 131 a and lower portion 133 a of trench 130 a are bothfilled with gate electrode layer 146 a. As described previously, sincetrench 130 a has a wider upper portion and conductive layer 134 has thesloped top surface, it may be easier for gate electrode layer 146 a tobe formed in trench 130 a. In some embodiments, gate electrode layer 146a is made of a conductive material, such as tungsten, aluminum, copper,titanium, tantulum, or other applicable materials.

After gate electrode layer 146 a is formed, a polishing process isperformed until the top surface of interlayer dielectric layer 128 isexposed, as shown in FIG. 1N in accordance with some embodiments. Insome embodiments, the polishing process is a chemical mechanicalpolishing process. As shown in FIG. 1N, a gate electrode structure 148 ais formed. Since gate electrode structure 148 a is formed in trench 130a, gate electrode structure 148 a also has a funnel shape in itscross-sectional view in accordance with some embodiments. In addition,conductive layer 134, conductive layer 136, and gate electrode structure148 a can be seen as a gate stack structure 150 a.

Afterwards, an etching-back process is performed on gate stack structure150 a, as shown in FIG. 1O in accordance with some embodiments. Duringthe etching-back process, the upper portion of gate electrode structure148 a and the upper portions of conductive layer 134 are etched. Arecess 152 is formed after the etching-back process is performed. Next,a hard mask structure 154 is formed in trench 152, as shown in FIG. 1Pin accordance with some embodiments. In some embodiments, hard maskstructure 154 formed over gate stack structure 150 and is made ofsilicon nitride.

FIG. 2 is a cross-sectional representation of semiconductor structure100 a illustrated along line A-A′ shown in FIG. 1P in accordance withsome embodiments. As shown in FIG. 2, semiconductor structure 100 aincludes gate stack structure 150 a formed across fin structure 110, andgate stack structure 150 a includes conductive layer 134, conductivelayer 136, and gate electrode structure 148 a.

As described previously, dummy gate structure 116 (as shown in FIG. 1F)may have a relatively small width for device size shrinkage, andtherefore gate stack structure 150 a may also have a relatively smallwidth. In some embodiments, gate stack structure 150 a has a width in arange from about 10 nm to about 25 nm. However, although the width ofgate stack structure 150 a is relatively small, the size of gateelectrode structure 148 a can still be relatively large since secondetching process 144 a is performed to remove the upper portion ofconductive layer 136 so that the space for forming gate electrodestructure 148 a is enlarged.

As shown in FIG. 2, gate electrode structure 148 a has a funnel shape inits cross-sectional view in accordance with some embodiments. Inaddition, gate electrode structure 148 a includes a first portion 156 a,a second portion 158 a, and a third portion 160 a in accordance withsome embodiments. First portion 156 a is located over second portion 158a, and second portion 158 a is located over third portion 160 a. In someembodiments, second portion 158 a has a trapezoid shape in itscross-sectional view.

As shown in FIG. 2, conductive layer 136 is formed around second portion158 a and third portion 160 a but is not formed over the sidewalls offirst portion 156 a of gate electrode structure 148 a in accordance withsome embodiments. In addition, conductive layer 134 is located aroundconductive layer 136 and extends over the sidewalls of first portion 156a in accordance with some embodiments.

As described previously, second etching process 144 a is performed, sothat gate electrode structure 148 a can have a wide upper portion (e.g.first portion 156 a.) As shown in FIG. 2, the width of the top surfaceof gate electrode structure 148 a (e.g. the width of the top surface offirst portion 156 a) is greater than the width of the bottom surface ofgate electrode structure 148 a (e.g. the width of the bottom surface ofthird portion 160 a or the width of the bottom surface of second portion158 a) in accordance with some embodiments. In some embodiments, thewidth of the top surface of first portion 156 a is greater than thewidth of the bottom surface of second portion 158 a.

In some embodiments, the width of the top surface of gate electrodestructure 148 a is in a range from about 5 nm to about 300 nm. In someembodiments, the width of the bottom surface of gate electrode structure148 a is in a range from 1 Å to about 300 nm. As described previously,the upper portions of conductive layer 136 is removed, so the space forforming gate electrode structure 148 e is enlarged and has a greaterupper portion. Therefore, gate electrode structure 148 e formed in theenlarged spacer also has the larger upper portion (e.g. first portion156 a), and the resistance of gate stack structure 150 a may be reducedaccordingly.

Furthermore, since second etching process 144 a is performed, conductivelayer 136 has the sloped top surface, which can also be seen as thesidewall of second portion 158 a of gate electrode structure 148 a. Asshown in FIG. 2, the sidewall of first portion 156 a has a firstinclination, the sidewall of second portion 158 a has a secondinclination, and the sidewall of third portion 160 a has a thirdinclination. The first inclination, the second inclination, and thethird inclination are different from one another in accordance with someembodiments.

In some embodiments, an angle between the sidewall of first portion 156a and the sidewall of second portion 158 a is in a range from about 95°to about 175°. In some embodiments, an angle between the sidewall ofsecond portion 158 a and the sidewall of third portion 160 a is in arange from about 95° to about 175°. Gate electrode structure 148 a isformed with such a shape, so that the filling of gate electrode layer146 a can be easier and the risk of forming gaps during the depositingprocess may be reduced.

In some embodiments, first portion 156 a has a thickness T₁ in a rangefrom about 0 nm to about 100 nm. In some embodiments, first portion 156a has a thickness T₁ in a range from about 2 nm to about 100 nm. In someembodiments, second portion 158 a has a thickness T₂ in a range fromabout 2 nm to about 50 nm. In some embodiments, third portion 160 a hasa thickness T₃ in a range from about 2 nm to about 50 nm. By performingsecond etching process 144 a, the size of gate electrode structure 148 amay also be enlarged, and the resistance of the resulting gate stackstructure 150 a can be reduced.

FIGS. 3A to 3B are cross-section representations of forming asemiconductor structure 100 b in accordance with some embodiments.Semiconductor structure 100 b is similar to semiconductor structure 100a, except an additional conductive layer is formed. Materials andprocesses used to form semiconductor structure 100 b may be similar to,or the same as, those used to form semiconductor structure 100 adescribed previously and are not repeated herein.

More specifically, processes shown in FIGS. 1A to 1H may be performed.After conductive layer 134 and conductive layer 136 are formed in thetrench 130 b, an additional conductive layer 236 is formed overconductive layer 136 in accordance with some embodiments. Next, ablocking structure 142 b may be formed at a lower portion 133 b oftrench 130 b, and a second etching process 144 b may be performed. Insome embodiments, second etching process 144 b is a wet etching process.During second etching process 144 b, conductive layer 236 and conductivelayer 134 are both etched to enlarge the space for depositing a gateelectrode layer later on. Afterwards, processes shown in FIGS. 1L to 1Pmay be performed to form semiconductor structure 100 b.

As shown in FIG. 3B, semiconductor structure 100 b includes a gate stackstructure 150 b formed across fin structure 110 over a substrate (e.g.substrate 102), and gate stack structure 150 b includes conductive layer134, conductive layer 136, conductive layer 236, and a gate electrodestructure 148 b. Gate electrode structure 148 b includes a first portion156 b, a second portion 158 b, and a third portion 160 b. In addition,hard mask structure 154 is formed over gate stack structure 150 b. Insome embodiments, conductive layer 236 is made of Ti_(x)N_(y), W,Ti_(x)Al_(y), Ti_(x)Al_(y)N, Ta_(x)Al_(y), Ta_(x)Al_(y)N_(z),Ti_(x)Si_(y)N_(z), Ta_(x)Si_(y)N_(z), Ta_(x)N_(y), Hf_(x)O_(y),Ti_(x)Ta_(y)N_(z). In addition, conductive layers 134, 136, and 236 aremade of different materials in accordance with some embodiments.

Since second etching process 144 b is performed to conductive layer 136and conductive layer 236, conductive layer 136 and conductive layer 236may have sloped top surfaces, which may help the deposition of the gateelectrode layer formed thereon. In addition, by performing secondetching process 144 b, the space for forming gate electrode structure148 b is enlarged, and therefore gate electrode structure 148 b isenlarged. By forming gate stack structure 150 b having larger gateelectrode structure 148 b, the resistance of gate stack structure 150 bcan be reduced, and the performance of semiconductor structure 100 b maybe improved.

FIGS. 4A to 4B are cross-section representations of forming asemiconductor structure 100 c in accordance with some embodiments.Semiconductor structure 100 c is similar to semiconductor structure 100a, except both conductive layers are etched during the second etchingprocess. Materials and processes used to form semiconductor structure100 c may be similar to, or the same as, those used to formsemiconductor structure 100 a described previously and are not repeatedherein.

More specifically, processes shown in FIGS. 1A to 1J may be performed.After a blocking structure 142 c is formed in the lower portion of atrench 130 c over a conductive layer 134′ and conductive layer 136, asecond etching process 144 c is performed in accordance with someembodiments. In some embodiments, conductive layer 134′ is made ofTi_(x)N_(y), W, Ti_(x)Al_(y), Ti_(x)Al_(y)N, Ta_(x)Al_(y),Ta_(x)Al_(y)N_(z), Ti_(x)Si_(y)N_(z), Ta_(x)Si_(y)N_(z), Ta_(x)N_(y),Hf_(x)O_(y), Ti_(x)Ta_(y)N_(z). In addition, conductive layers 134′ and136 are made of different materials in accordance with some embodiments.During second etching process 144 c, both conductive layer 134′ andconductive layer 136 are etched. Afterwards, processes shown in FIGS. 1Lto 1P may be performed.

As shown in FIG. 4B, semiconductor structure 100 c includes a gate stackstructure 150 c formed across fin structure 110 over a substrate, andgate stack structure 150 c includes conductive layer 134′, conductivelayer 136, and gate electrode structure 148 c. Gate electrode structure148 c includes a first portion 156 c, a second portion 158 c, and athird portion 160 c. In addition, hard mask structure 154 is formed overgate stack structure 150 c.

Since second etching process 144 c is performed to both conductive layer134′ and conductive layer 136, conductive layer 134′ and conductivelayer 136 may both have sloped top surfaces. The sloped top surface mayhelp the deposition of the gate electrode layer formed thereon. Inaddition, by performing second etching process 144 c, the space forforming gate electrode structure 148 c is enlarged, and therefore gateelectrode structure 148 c formed in the space is enlarged. By forminggate stack structure 150 c having larger gate electrode structure 148 c,the resistance of gate stack structure 150 c can be reduced, and theperformance of semiconductor structure 100 c may be improved.

FIGS. 5A to 5B are cross-section representations of forming asemiconductor structure 100 d in accordance with some embodiments.Semiconductor structure 100 d is similar to semiconductor structure 100a, except only one conductive layer is formed. Materials and processesused to form semiconductor structure 100 d may be similar to, or thesame as, those used to form semiconductor structure 100 a describedpreviously and are not repeated herein.

More specifically, processes shown in FIGS. 1A to 1H may be performed.However, only one conductive layer 136′ is formed in a trench 130 d inaccordance with some embodiments. In some embodiments, conductive layer136′ is made of Ti_(x)N_(y), W, Ti_(x)Al_(y), Ti_(x)Al_(y)N,Ta_(x)Al_(y), Ta_(x)Al_(y)N_(z), Ti_(x)Si_(y)N_(z), Ta_(x)Si_(y)N_(z),Ta_(x)N_(y), Hf_(x)O_(y), Ti_(x)Ta_(y)N_(z). After conductive layer 136′is formed, a blocking structure 142 d is formed in the lower portion oftrench 130 d, and a second etching process 144 d is performed to etchthe upper portion of conductive layer 136′. After second etching process144 d is performed, process shown in FIGS. 1L to 1P may be performed.

As shown in FIG. 5B, semiconductor structure 100 d includes a gate stackstructure 150 d formed across fin structure 110 over the substrate, andgate stack structure 150 d includes conductive layer 136′ and gateelectrode structure 148 d. In addition, hard mask structure 154 isformed over gate stack structure 150 d.

Similarly, conductive layer 136′ also has sloped top surfaces andenlarged gate electrode structure 148 d, and therefore the resistance ofgate stack structure 150 d can be reduced, and the performance ofsemiconductor structure 100 d may be improved.

FIGS. 6A to 6D are cross-sectional representations of various stages offorming a semiconductor structure 100 e in accordance with someembodiments. Some materials and processes used to form semiconductorstructure 100 e may be similar to, or the same as, those used to formsemiconductor structure 100 a and are not repeated herein.

A structure similar to that shown in FIG. 4A may be formed, and themethod to form the structure may be similar to, or the same as, thosedescribed previously. More specifically, a dummy gate structure isformed across fin structure 110 over a substrate, and spacers 122,contact etch stop layer 126, and interlayer dielectric layer 128 areformed around the dummy gate structure. Next, the dummy gate structureis removed to form a trench 130 e between spacers 122, and a conductivelayer 634 and a conductive layer 636 are formed over the bottom and thesidewalls of trench 130 e. In some embodiments, conductive layer 634 andconductive layer 636 are individually made of Ti_(x)N_(y), W,Ti_(x)Al_(y), Ti_(x)Al_(y)N, Ta_(x)Al_(y), Ta_(x)Al_(y)N_(z),Ti_(x)Si_(y)N_(z), Ta_(x)Si_(y)N_(z), Ta_(x)N_(y), Hf_(x)O_(y),Ti_(x)Ta_(y)N_(z). In some embodiments, conductive layer 634 andconductive layer 636 are made of different materials.

Afterwards, a blocking structure 142 e is formed in the lower portion oftrench 130 e and a second etching process 144 e is performed to etchconductive layer 634 and conductive layer 636. As shown in FIG. 6A,after second etching process 144 e is performed, conductive layer 634and conductive layer 636 have sloped top surfaces in accordance withsome embodiments.

Next, block structure 142 e is removed, and trench 130 e now includes anupper region 130 e and a lower portion 133 e, as shown in FIG. 6B inaccordance with some embodiments. As shown in FIG. 6B, lower portion 133e of trench 130 e is surrounded by conductive layer 636. Afterwards,another conductive layer 638 is formed in trench 130 e, as shown in FIG.6C in accordance with some embodiments. In some embodiments, conductivelayer 638 is made of Ti_(x)N_(y), W, Ti_(x)Al_(y), Ti_(x)Al_(y)N,Ta_(x)Al_(y), Ta_(x)Al_(y)N_(z), Ti_(x)Si_(y)N_(z), Ta_(x)Si_(y)N_(z),Ta_(x)N_(y), Hf_(x)O_(y), Ti_(x)Ta_(y)N_(z). In some embodiments,conductive layers 634, 636, and 638 are made of different materials.

More specifically, conductive layer 638 covers the upper portion of thesidewalls of trench 130 e, the slopes top surfaces of conductive layer634 and conductive layer 636, and the sidewalls of conductive layer 636.In some embodiments, lower portion 133 e of trench 130 e is fully filledwith conductive layer 638. That is, conductive layer 638 has anextending portion surrounding by conductive layer 636 in accordance withsome embodiments.

After conductive layer 638 is formed, processes similar to those shownin FIGS. 1M to 1P may be performed to form semiconductor structure 100e. As shown in FIG. 6D, semiconductor structure 100 e includes a gatestack structure 150 e formed across fin structure 110 over thesubstrate, and gate stack structure 150 e includes conductive layer 346,conductive layer 636, conductive layer 638, and gate electrode structure148 e. Gate electrode structure 148 e includes a first portion 156 e anda second portion 158 e. In addition, hard mask structure 154 is formedover gate stack structure 150 e.

In some embodiments, second portion 158 e has a tip bottom portion. Insome embodiments, second portion 158 e has a triangular shape in itscross-sectional view. As shown in FIG. 6D, conductive layer 638 ispositioned between conductive layer 636 and gate electrode structure 148e and covers the sidewalls of first portion 156 e and second portion 158e.

By performing second etching process 144 e, the upper portion ofconductive layer 634 and conductive layer 636 are removed. Therefore,after conductive layer 638 is formed, upper portion 131 e of trench 130e can still have enough space for forming gate electrode structure 148e, although lower portion 133 e of trench 130 e is filled withconductive layer 638. Accordingly, even if the width of gate stackstructure 150 e is relatively narrow, a number of conductive layers maystill be formed in lower portion 131 e of trench and there will still beenough space for gate electrode structure 148 e to be formed.

It should be noted that although some structures shown in the figuresand described previously are divided into several portions, they aredrawn and described for better understanding the concept of thedisclosure. However, there may not be actual boundaries or interfacesbetween them. In addition, in various embodiments, a gate stackstructure may include one or more conductive layers, and the scope ofthe disclosure is not intended to be limiting.

As described previously, a gate stack structure (e.g. gate stackstructure 150 a to 150 e) includes a conductive layer (e.g. conductivelayers 134, 136, 236, 134′, 136′, 634, 636, and 638) and a gateelectrode structure (e.g. gate electrode structures 148 a to 148 e)formed over the conductive layer in accordance with some embodiments. Inaddition, before the gate electrode structure is formed, an etchingprocess (e.g. second etching processes 144 a to 144 e) is performed, sothat the space for forming the gate electrode layer is enlarged.Therefore, the gate stack structure can have a larger gate electrodestructure, such as made of tungsten, and therefore the resistance of thegate stack structure can be reduced.

In addition, a hard mask layer (e.g. hard mask layer 154) is formed overthe gate stack structure in accordance with some embodiments. Since theetching process is performed to enlarge the space of the upper portionof the gate stack structure, there also is enough space for forming thehard mask layer. Therefore, the risk for forming short circuit due tothin hard mask layer can be reduced. In addition, even if the hard masklayer is formed, the remaining gate electrode structure can still have asufficient size, and the performance of the gate stack structure may beimproved.

Furthermore, in some embodiments, the etching process is a wet etchingprocess. When several conductive layers are formed, the wet etchingprocess may have a better etching selectively towards each conductivelayer. In addition, after the etching process, the conductive layer mayhave a sloped top surface, which may help the forming of the gateelectrode layer (e.g. gate electrode layer 146 a) formed over it.Moreover, by performing the wet etching process, the risks of shorteningthe gate stack height due to etching may also be reduced.

Embodiments of a semiconductor structure and methods for forming thesemiconductor structures are provided. The semiconductor structureincludes a gate stack structure. The gate stack structure includes agate electrode structure and a conductive layer formed below the gateelectrode structure. The gate electrode structure includes a wide upperportion and a narrow lower portion, so that the resistance of the gatestack structure may be reduced. Therefore, the performance of the gatestack structure may be improved.

In some embodiments, a semiconductor structure is provided. Thesemiconductor structure includes a gate stack structure formed over asubstrate. The gate stack structure includes a gate electrode structurehaving a first portion and a second portion and a first conductive layerbelow the gate electrode structure. In addition, the first portion ofthe gate electrode structure is located over the second portion of thegate electrode structure, and a width of a top surface of the firstportion of the gate electrode structure is greater than a width of abottom surface of the second portion of the gate electrode structure.

In some embodiments, a semiconductor structure is provided. Thesemiconductor structure includes a fin structure formed over a substrateand a gate stack structure formed across the fin structure, the gatestack structure includes a gate electrode structure having a firstportion, a second portion located below the first portion, and a thirdportion located below the second portion and a first conductive layerformed around the second portion and the third portion of the gateelectrode structure. In addition, a width of a top surface of the firstportion of the gate electrode layer is greater than a width of a bottomsurface of the third portion of the gate electrode layer.

In some embodiments, a method for manufacturing a semiconductorstructure is provided. The method for manufacturing a semiconductorstructure includes forming a trench over a substrate and forming a firstconductive layer on sidewalls and a bottom of the trench. The method formanufacturing a semiconductor structure further includes forming a hardmask layer over the first conductive layer and etching the hard masklayer to form a blocking structure in a lower portion of the trench byperforming a first etching process. The method for manufacturing asemiconductor structure further includes etching a portion of the firstconductive layer not covered by the blocking structure by performing asecond etching process and removing the blocking structure. The methodfor manufacturing a semiconductor structure further includes filling thetrench by a gate electrode layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for manufacturing a semiconductorstructure, comprising: forming a trench in a dielectric layer over asubstrate; forming a first conductive gate layer on sidewalls and abottom of the trench; forming a hard mask layer over the firstconductive layer; performing a first etching process including etchingthe hard mask layer to form a blocking structure in a lower portion ofthe trench, wherein an uppermost surface of the blocking structure isbelow a top surface of the dielectric layer; etching a portion of thefirst conductive gate layer not covered by the blocking structure byperforming a second etching process to form an etched portion of thefirst conductive gate layer, wherein a sloped top surface of the etchedportion extends from a top surface of the blocking structure upwards toan underlying layer disposed under the first conductive gate layer inthe trench; removing the blocking structure; and after removing theblocking structure, forming a conductive material in the trench over theetched portion of the first conductive gate layer.
 2. The method formanufacturing a semiconductor structure as claimed in claim 1, whereinthe second etching process is a wet etching process.
 3. The method formanufacturing a semiconductor structure as claimed in claim 1, whereinthe first etching process is a dry etching process.
 4. The method formanufacturing a semiconductor structure as claimed in claim 1, furthercomprising forming the underlying layer as a second conductive gatelayer before the first conductive gate layer is formed, wherein thesecond conductive gate layer is not etched during the second etchingprocess.
 5. The method for manufacturing a semiconductor structure asclaimed in claim 4, further comprising forming a third conductive gatelayer over the first conductive gate layer after the blocking structureis removed, wherein the conductive material is formed over the thirdconductive gate layer.
 6. The method for manufacturing a semiconductorstructure as claimed in claim 1, wherein the conductive material forms astructure having a first portion and a second portion located below thefirst portion, and a width of a top surface of the first portion of thestructure is greater than a width of a bottom surface of the secondportion of the structure.
 7. The method for manufacturing asemiconductor structure as claimed in claim 1, forming the trench in thedielectric layer comprises: forming a fin structure over the substrate;forming a dummy gate structure across the fin structure; forming spacerson sidewalls of the dummy gate structure; and removing the dummy gatestructure to form the trench.
 8. The method for manufacturing asemiconductor structure as claimed in claim 1, further comprising:forming a second conductive layer before the first conductive layer isformed, wherein the second conductive layer is not etched when theportion of the first conductive layer not covered by the blockingstructure is etched.
 9. The method for manufacturing a semiconductorstructure as claimed in claim 8, wherein a portion of the secondconductive layer is contact with the conductive gate layer.
 10. A methodfor manufacturing a semiconductor structure, comprising: forming atrench in a dielectric layer over a substrate; forming a firstconductive layer on sidewalls and a bottom of the trench; forming asecond conductive layer over the first conductive layer, the sidewallsand the bottom of the trench; depositing a hard mask material over thesubstrate; etching back the hard mask material such that an uppermostsurface of the hard mask material is below a top surface of thedielectric layer thereby forming a blocking structure in a lower portionof the trench to cover the first conductive layer and the secondconductive layer at a lower portion of the trench; etching a portion ofthe first conductive layer not covered by the blocking structure,wherein the etching forms a sloped top surface of the first conductivelayer after the portion of the first conductive layer not covered by theblocking structure is etched, wherein the sloped top surface extendsfrom a top surface of the blocking structure upwards to an interfacewith the second conductive layer; after the etching the portion of thefirst conductive layer, removing the blocking structure; and filling thetrench by a conductive gate layer.
 11. The method for manufacturing asemiconductor structure as claimed in claim 10, wherein the portion ofthe first conductive layer not covered by the blocking structure isetched by performing a wet etching process.
 12. The method formanufacturing a semiconductor structure as claimed in claim 10, whereina gate electrode structure including the conductive gate layer has afunnel shape in its cross-sectional view.
 13. A method for manufacturinga semiconductor structure, comprising: forming a trench in a dielectriclayer over a substrate; forming a first conductive layer and a secondconductive layer on sidewalls and a bottom of the trench; forming a hardmask layer over the first conductive layer and the second conductivelayer; etching back the hard mask layer to form a blocking structurewithin the trench over the first and second conductive layers, whereinthe etching back exposes a lateral surface of the first conductive layerparallel the sidewall of the trench; performing an etching processincluding etching an upper portion of the first conductive layerincluding the lateral surface, but not etching the second conductivelayer, wherein the etching process forms a sloped top surface of thefirst conductive layer disposed above the etched back hard mask layerwherein the sloped top surface extends from a top surface of theblocking structure upwards to an interface with the second conductivelayer; and forming a gate electrode layer in the trench.
 14. The methodfor manufacturing a semiconductor structure as claimed in claim 13,wherein the gate electrode layer is in contact with a portion of thesecond conductive layer and a portion of the first conductive layer. 15.The method for manufacturing a semiconductor structure as claimed inclaim 13, wherein the etching process is a wet etching process.
 16. Themethod for manufacturing a semiconductor structure as claimed in claim13, wherein a width of an upper portion of the gate electrode layer isgreater than a width of a bottom portion of the gate electrode layer.